The US space agency's rovers will get a software upgrade to allow them to make "intelligent" decisions in the study of Martian clouds and dust devils.

The new algorithms will give the robots' computers the onboard ability to search through their images to find pictures that feature these phenomena.

Only the most significant data will then be sent to Earth, maximising the scientific return from the missions.

Nasa says its robotic craft will become increasingly autonomous in the future.

"An instrument can acquire considerably more data than can be down-linked - this is a recurring theme on all spacecraft," explained Rebecca Castano, from the agency's Jet Propulsion Laboratory (JPL).

In the future, the capability will be there not just to patch flight software but to completely re-write it

Ralph Lorenz, University of Arizona

"The idea now is to collect as much data as the instrument can, analyse them onboard for features of specific interest, and then down-link only the data that have the highest priority," she told BBC News.

Currently, the rovers are allocated time to look for clouds and dust devils, which may or may not appear - they are naturally transient events. And getting humans to sift the images is time consuming.

The software upgrade, due to take place in the next month, will make the whole process much more efficient.

"Clouds typically occur in 8-20% of the data collected right now," Castano said.

"If we could look for a much more extended time and select only those images with clouds then we could increase our understanding of how and when these phenomena form. Similarly with the dust devils."

Quick reactions

Leaving the robots to "get on with it" - to do the decision-making - is the way ahead, Nasa believes.

The agency's Mars Odyssey orbiter, which has been mapping the Red Planet since 2001, will get new autonomous flight software later this year.

Distant Erebus: Scientists were alerted rapidly to the event

This will give the satellite the ability to react to sudden changes on the Martian surface. It will be "tuned" to look for temperature anomalies, rapid changes in the polar caps, the emergence of dust storms and the formation of water-ice clouds.

If its algorithms mark an event of interest, the spacecraft will be able to break into its routine and take more images, without waiting for commands from Earth.

Scientists say this will capture short-lived, but highly significant, events that might otherwise have been missed.

The approach has been pioneered on Nasa's Earth Observing-1 satellite, which has now made thousands of autonomous data collections since 2003.

Operational costs on EO-1 have been reduced dramatically

A classic example was an eruption on Antarctica's Mt Erebus volcano in 2004. Typically, it could take several weeks to learn such a remote volcano had gone into an active phase; but as soon as EO-1 detected heat from the lava lake at the mountain's summit, it reprogrammed its camera to take more pictures.

The spacecraft also sent a rapid alert to volcanologists on the mission's science team.

So successful has EO-1's Autonomous Sciencecraft Experiment software been that it is now running the satellite's main science operations.

"This has helped us reduce the operations cost of this mission from $3.6m to $1.6m a year - over half that reduction was directly attributed to the onboard automation that we're talking about. That was critical in getting the mission extended," said Steve Chien, principal investigator for autonomous sciencecraft at JPL.

"The approach has shown its worth and it is applicable to a wide range of future missions."

Distant control

Ralph Lorenz, from the University of Arizona, Tucson, works on the current Cassini-Huygens mission to Saturn and its moons.

He was thrilled by the performance of the Huygens lander, which touched down on the ringed planet's largest satellite, Titan, in January 2005; and he is already thinking about a return flight some time in the next decade.

On distant worlds, autonomous flight control could be essential

He said self-reliant spacecraft would open up new science opportunities on far-distant missions, where probes might be out of contact with Earth for hours or even days at a time.

Lorenz envisages the next craft on Titan to be a blimp that could fly itself around the moon and select the most interesting locations to set down to do investigations.

"It's important to note also that launch dates will no longer limit technological capabilities," he added.

"We've seen how the Mars rovers are constantly being updated. To get to Titan, it will take about seven years, during which time we can improve and finesse the type of autonomous software we might apply. In the future, the capability will be there not just to patch flight software but to completely re-write it."

Castano, Chien and Lorenz were explaining the latest developments in autonomous spacecraft operations here at the American Geophysical Union Joint Assembly.